Process for treatment of mattes and sulphurated nickel concentrates

ABSTRACT

Nickel containing concentrates, particularly nickel matte, containing by weight 55 to 75 percent nickel, 10 to 40 percent sulphur and a minor proportion of secondary metals in powder or pulp form are subjected to an oxidizing lixiviation with nitric acid preferably in the presence of oxygen, nitrous vapors formed being regenerated to nitric acid and recycled. The solution from the oxidizing lixiviation is sulphated to substantially replace nitrate by sulphate; secondary metals, in particular iron, copper and cobalt are removed and pure hydrated nickel sulphate is crystallized from the solution. Preferably nickel hydroxide and carbonate are precipitated from the mother liquor from the crystallization of nickel sulphate and are used in the removal of iron and cobalt.

Gandon et al.

PROCESS FOR TREATMENT OF MATTES AND SULPHURATED NICKEL CONCENTRATESInventors: Louis Gandon; Roger Jean; Philippe Lenoble, all of Le Havre,France Assignee: Le Nickel, Paris, France Filed: Oct. 3, 1969 Appl. No.:863,569

Field ofSearch ..75/1l9,117,115,l21,101R, 75/109, 108; 23/183, 61, 200,117

References Cited UNITED STATES PATENTS Rankin ..75/101 X 1,212,3341/1917 Eustis ..75/119 X 1,756,092 4/1930 Lathe ..75/1l9 2,367,239l/l945 Renzoni ....75/119 2,377,832 6/1945 Wallis et al. ..23/l832,959,467 1l/1960 Yusuf et a1 ..75/l19 X Primary ExaminerL. DewayneRutledge Assistant Examiner-G. T. Ozaki Attorney-Oberlin, Maky, Donnelly& Renner [57] ABSTRACT Nickel containing concentrates, particularlynickel matte, containing by weight 55 to 75 percent nickel, 10 to 40percent sulphur and a minor proportion of secondary metals in powder orpulp form are subjected to an oxidizing lixiviation with nitric acidpreferably in the presence of oxygen, nitrous vapors formed beingregenerated to nitric acid and recycled. The solution from the oxidizinglixiviation is sulphated to substantially replace nitrate by sulphate;secondary metals, in particular iron, copper and cobalt are removed andpure hydrated nickel sulphate is crystallized from the solution.Preferably nickel hydroxide and carbonate are precipitated from themother liquor from the crystallization of nickel sulphate and are usedin the removal of iron and cobalt.

3 Claims, 1 Drawing Figure PATENTEDAPR '18 I972 3,656, 937

MATTE OR CONCENTRATE Puvscm. TREATMENT AIR WATER HNO5 N20 NITRIC ACIDHNO OX'DAT'ON REGENERATION 5 LBYEE m DENITRIFICATION AI IPSULPHUWMETMWATER ADJUSTMENT J Qa IRON REMOVAL SOLUTION Fem) }REJECT NICKEL POWDER w2( )5 C0(0H) REMOVL 0F Ni(OH) COBALT FILTRATION WATER RECYCLE Mm MOTHERLIQUORS PURE NICKEL T, SULFATE V N02 CO3 k REc|P\TAT|oN| @EUPTTATTONIINew FILTFSATION FILTFhTlON WATER wAEafnNs WA HlNG WATER WASTE WATER TNa$0 Na N03 REJECT NaCl PROCESS FOR TREATMENT OF MATTES AND SULPHURATEDNICKEL CONCENTRATES This invention relates to a process for thehydrometallurgical treatment of sulphurated nickel concentrates,especially the nickel mattes obtained after conventionalpyrometallurgical treatment of ores, with a view to recovering from themnot only the nickel but also other secondary metals of commercialsignificance, more particularly cobalt and copper which are usuallyassociated with nickel in concentrates of this kind.

Sulphurated nickel concentrates to which the treatment according to theinvention is applicable include those which generally contain from 55 to75 percent of nickel and from to 40 percent of sulphur, thesepercentages being given by weight, like all those which will follow inthe present specificatron.

Examples of mattes capable of undergoing the treatment according to theinvention include the mattes produced by the pyrometallurgical processworked at the DONIAMBO factory of LE NICKEL, NOUMEA (New Caledonia),emanating from the sulfurizing fusion in a low-shaft furnace of a nickeloxide ore called garnierite. The crude matter thus obtained is refinedin converters of the BESSEMER type wherein the iron is burnt out by anair blast and scorified by the silica introduced during blasting. Themattes in question generally contain from 22 to 28 percent of sulphur,from 71 to 73 percent of nickel, from 1.5 to 5 percent of iron and from2 to 5 percent of cobalt, in addition to small quantities of otherelements including copper, manganese, aluminum, magnesium and silica.

Examples of hydrometallurgically sulphurized concentrates lendingthemselves to the treatment according to the invention include thoseobtained by precipitation with hydrogen sulfide from sulphuric solutionswhich have been used for the lixiviation of laterites, for example, thesulphurized concentrates manufactured in the Cuban MOA-BAY works. Amaterial of this kind usually has the following composition on a dryweight basis:

nickel 52 to 68% cobalt 5 to 6% Copper 0.5 to 1% iron 1 to 1.5% zinc lto 1.5% sulphur 30 to 38% The other impurities consist of manganese,magnesia, alkaline-earth metals, silica, in a total quantity notexceeding 1 percent.

In addition, the initial products capable of being treated in accordancewith the invention are not necessarily intermediate products obtained byan initial concentration of ores. For example, they can be mixturesemanating by precipitation with hydrogen sulfide from impure nickelsolutions as are obtained in processes for regenerating nickel-platingbaths or hydrogenation catalysts, or even materials emanating from thepyrometallurgical treatment of slags with sulphur with a view toconcentrating the metals present in them.

i It has long been known to subject sulphurized concentrates of theaforementioned type to an acid or basic lixiviation to dissolve themetals, generally in the form of salts, to enable them to besubsequently extracted in pure form. There are two general methods oftreatment in common use, namely ammonical lixiviation in which asolution of ammonia and arm monium carbonate is used as the lixiviatingagent, and sulphuric acid lixiviation. Both these methods have thedisadvantage that the initial concentrate has to be subjected to anattack which is as long as it is difficult and which in addition usuallyhas to be carried out under pressure.

The ammonical lixiviation method also has the disadvantage of convertingthe sulphur present into complexes which are all the more difficult toseparate if they consist of thionates or polythionates. A second stageof oxidation under pressure or of hydrolysis by prolonged boiling isnecessary for the reconversion of these complexes. In addition, themetals are extracted in the form of amines and have to be collected inammonia recovery and distillation systems which use up a considerableamount of energy.

Apart from difficulties arising out of the use of sulphuric acid indilute fonn under pressure, the sulphuric lixiviation process does notlead to high yields and the lixiviation stages have to be increased innumber if it is desired to obtain economically acceptable yields.

The present invention provides an improved process for thehydrometallurgical treatment of mattes and concentrates of theaforementioned type which obviates the disadvantages affectingconventional processes, is easier and less expensive to carry intooperation and gives a higher yield.

The process according to the invention comprises the steps of:

i. subjecting the finely comminuted nickel containing concentrate to anoxidizing lixiviation with nitric acid, nitrous vapours formed in thisstage being regenerated into nitric acid which is recycled;

ii. subjecting the solution produced from the oxidizing lixiviationstage to hydration or sulphation to substantially replace nitrate in thesolution by sulphate;

iii. subjecting the solution produced from the hydration or sulphationstage to successive treatment stages in which the secondary metals areseparated to leave a solution with nickel as substantially the onlyremaining cation; and

iv. recovering nickel from the residual solution by crystallization inthe form of pure hydrated nickel sulphate.

If necessary the nickel containing concentrate is subjected to aninitial physical treatment to convert it to the finely comminuted formsuitable for the oxidizing lixiviation.

The most important aspect of the invention is the oxidizing lixiviationwith nitric acid in which the nitric acid performs the simple functionof an oxygen-transfer agent. This stage is preferably carried out in thepresence of a free-oxygen containing gas. The main advantage of thismethod is embodied in the fact that the oxidation reactions involvingthe nitric acid are exothermic with the result that the process onlyrequires a minimum supply of energy from outside so that it isparticularly economic to operate.

The nitric lixiviation is preferably carried out at atmospheric pressurewith stirring in air at a temperature below the boiling temperature ofnitric acid. All these features contribute to the economy of the processaccording to the invention from a practical point of view.

Any conventional methods may be used for the subsequent separation ofthe secondary metals, in particular iron, copper and cobalt. Forexample, the cobalt may be precipitated in the form of cobalt (Ill)hydroxide by treatment with an alkali metal or alkaline-earth metalhypochlorites or with chlorine in the presence of nickel (II) hydroxideor nickel carbonate. According to one important aspect of the invention,however, the secondary metals are preferably separated by operationswhich do not totally reduce the nickel content of the sulphated brine,namely separation of the iron by the action of nickel (II) carbonateobtained from the mother liquors, separation of the copper bycementation through the addition of nickel powder, and separation of thecobalt by the addition of nickel (III) hydroxide obtained by treatingthe residual mother liquors. Thus the process according to the inventionmay be referred to as a loop process in which the nickel which is notrecovered in the form of pure sulphate is continuously recycled, whichis a factor of economic significance.

So far as the preparatory physical treatment is concerned, to transformsolid products into a suspension, for example mattes, the startingmaterial is initially crushed to convert it into a relatively finepowder. Crushing should not be over done because on the one hand theoxidizing lixiviation with nitric acid is extremely effective and on theother hand introduction of an excessively fine material into the nitricacid gives rise to the formation of a foam or froth which interfereswith the normal operation of any installation. It has been found thatthe best results are obtained with a powder percent of whose grains arebetween and 200 microns in size.

In the case of concentrates obtained by wet precipitation, thepreparatory phase merely comprises dispersion in water to convert theminto a homogeneous pulp which is fluent enough to be continuouslyintroduced into the reaction medium.

The accompanying drawing shows a flow-sheet illustrating the processaccording to the invention in its preferred embodiment in which thenickel from the residual mother liquors is recycled in the form ofnickel carbonate and nickel (III) hydroxide.

As shown in the flow-sheet following the initial physical treatment, theprocess comprises the following stages:

introduction of the finely comminuted concentrate into a nitric acidsolution with cyclic recovery of the nitrous vapours produced and theirreconversion into nitric acid by oxidation in air,

adjustment of the sulphur: metal ratio to obtain a true sulphate brineby addition of sulphuric acid,

separation by filtration of any insoluble materials resulting from thesetreatments,

precipitation of iron with nickel carbonate and separation by filtrationof the ferric carbonate formed separation of the copper by cementationwith powdered nickel and recovery by filtration of the copperprecipitated, elimination of the cobalt by double decomposition withnickel (III) or nickel carbonate converting the cobalt sulphate intoinsoluble cobalt (III) hydroxide or cobalt carbonate and separatingthese precipitates by filtration,

separation of pure nickel in sulphate form by crystallization afterconcentration of the brine; the mother liquor containing traces ofnitrate which have been formed are themselves converted by doubledecomposition into either nickel (II) carbonate and nickel (III)carbonate or into nickel (III) hydroxide which is returned to thecircurt.

The compounds to be treated are introduced into a nitric acid solutionwhose concentration may vary within certain limits, although the bestresults are obtained with solutions whose concentration is around 50percent.

The reactor is kept at a temperature above 60 C., and below the boilingpoint of nitric acid, preferably 80 C. A vigorous current of air bubblesthrough the reaction medium being necessary to accelerate elimination ofthe nitrous gases. The nitrous gases are introduced into an absorptionand oxidation tower which reconverts them into a nitric acid solutionwhich is returned to the circuit. This installation is similar to thatused in nitric acid manufacturing plants.

The main chemical reactions which underlie these operations are asfollows:

1. M S 4l-INO M"*SO 2N O t+ 2H O 2. 3N O H O 2I-INO 4N0 3. 4N0 2N O andthe cycle begins again.

The brine resulting from this treatment is subjected to a hydrationtreatment and, optionally to a, sulphuration treatment. This treatmentcomprises adding the sulphuric acid required to neutralize the basicsulphates if an initial material unsaturated with sulphur is used, forexample the nickel mattes from New Caledonia. The effect of thesulphuric acid is instantaneous when the temperature is around theboiling point. This sulphation treatment also has a secondary function,namely to displace the nitrates because they are not very stable at thetemperature at which this treatment is carried out. 1

Assuming that a nickel matte has the approximate formula Ni S (26.7percent of sulphur), nitric oxidation in the presence with air will leadto a product of the formula:

This material is converted into the neutral sulphate by the followingreaction:

On the other hand, a small proportion of this subsulphide is convertedinto nickel nitrate Ni(NO Under the operating conditions selected, thisgives rise to a displacement in accordance with the simplified reaction:

The solution which results from this treatment and which issubstantially denitrified is subjected to a filtration whose function itis to eliminate the small amount of residual sulphur, that proportion ofthe iron hydroxide already precipitated and above all insolublerefractory components such as silica in particular.

The filtrate is then delivered into a tank where its pI-I-value isadjusted with a view to precipitating the ferric iron. This operation isbest carried out by adding nickel carbonate and the iron which was inthe ferric state precipitates completely at about pH 4.

The reaction can be formulated as follows:

The ferric compound thus formed is then separated by filtration. Theresulting solution is then treated with nickel (Ill) hydroxide toprecipitate the cobalt (III) hydroxide in accordance with the followingreaction:

In the preferred embodiment of the invention in which nickel (II)carbonate is used for precipitating the iron and nickel (III) hydroxidefor precipitating the cobalt, filtration of the cobalt (III) hydroxideleaves a saline solution whose cation is solely nickel whilst the anionsconsist of a mixture of nitrate and sulphate in which it issubstantially the sulphate component which predominates. The finalpurification stage comprises a selective crystallization followingevaporation of the brine. In effect, the nickel sulphate remains muchmore insoluble than the corresponding nitrate and almost all the nickelis readily separated in the form of a pure hydrated sulphate. The motherliquors which contain all the nitrate and a little sulphate are thenrecovered in the form of nickel carbonate and hydroxide which arereturned to the circuit and which are used to precipitate the iron andthe cobalt, respectively. The reactions involved are as follows:

1. Ni(NO Na CO 2NaNO NiCO t The insoluble nickel carbonate is filteredand washed until the sodium ions have been removed. 2. 2Ni(NONaOCl-l-4NaOl-I H O 2Ni(OH) NaCl 4NaNO3 The nickel (III) hydroxide isfiltered and washed in boiling water until the chlorine and sodium ionshave disappeared. It is then used to precipitate the cobalt. Thus it canbe seen that the cycle is completely in the form of a loop. Naturallythe nickel sulphate obtained in a perfectly pure form can be convertedinto pure nickel by conventional processes.

The invention is illustrated by the following Examples:

EXAMPLE 1 The apparatus used consists of a three-liter-capacity glassreactor equipped with a stirrer and a thermometer and also surmounted bya condenser which opens into a column packed with Raschig ringscomprising several stages separated by nozzles for the introduction ofair. The reactor is also provided with means for introducing thereactants. The reactor itself is placed in a thermostatically controlledcabinet by means of which the reacting mixture can be heated and cooled.

The packed column is continuously washed with a recycled solution, thedownward circulation of the liquid being ensured by means of a pump.919.5 g of 10.95N nitric acid of specific gravity 1.30 are introducedinto the reactor. After the acid has been introduced, 20 liters of airper hour are bubbled through it. The temperature is raised to C. and 300g of nickel matte are introduced over a period of 1 hour and 40 minutes,the temperature being kept at C. throughout the entire operation. Thematte treated has the following weight analysis:

Ni 71.88% Co 2.48% Fe 5.20% Cu 0.028%

Insoluble components such as metal silicates and silica 0.243%

GRANULOMETRY:

Eighty percent of the grains are unable to pass through a 100p. screenwhile all of them pass through a 200;; screen.

After the reactants have been introduced, stirring is continued and thetemperature kept at 90 C. over a period of 2% hours. Eight hundred andninety ml of a brownish-colored sludge-like suspension are obtained.Over a period of 1 hours and 45 minutes 367.7 g of 35N sulphuric acidwith a specific gravity of 1.86 are added to this suspension. Thetemperature is increased to 102 C. and deep red vapours escape inabundance towards the nitric acid regeneration column.

On completion of this operation, 461 g of water are added and thesuspension is filtered in a Buchner funnel. During this operation thetemperature is not reduced below 95 C. The residue collected on thefilter is washed repeatedly with 200 g of boiling water and all thefiltrates are collected and subjected to analysis. They weigh 1,970 g,have a specific gravity of 1.349 and a volume of 1,670 ml. After theirvolume has been increased to 2 liters by the addition of water at C.,their composition is as follows:

Ni 104.16 g/l Co 3.325 g/l Fe 7.625 g/l Cu 0.054 g/l NO 1.03(equivalent/ liter) The solid residue weighs 13 g and corresponds to thefollowing weight analysis:

Fe 0.82% Ni 0.43% SiO 5.5 8%

A portion of the preceding solution 1815 ml) is neutralized to pH 5.9 bythe addition of 230 g of nickel carbonate weighed dry but dispersed in694 g of water. Accordingly the iron is precipitated out as Fe(OI-I) andremoved by filtration. This operation is carried out at a temperature of50 to 60 C. with vigorous stirring. It is completed by the addition of99.6 mg of ultra-fine nickel powder (98.7 percent pure) in order toprecipitate the copper. In addition the oxidation-reduction potential isadjusted by the addition of 8.25 ml of N/50 1(Mn0. so as to eliminateevery risk of leaving iron or manganese in solution.

The dispersion obtained is filtered in a Buchner funnel at roomtemperature. There is obtained on the one hand a clear green solution ofnickel and cobalt in the form of sulfates weighing 2,500 g with aspecific gravity of 1.210 and on the other hand a precipitate weighing791 g. The precipitate is washed with 1,576 g of boiling water and isthen filtered which leads to two fractions:

i. a liquid fraction with a volume of 1985 ml containing 9.816 g/literof nickel; and

ii. a solid fraction weighing 654.5 g and containing on a dry basis 2.28percent of nickel, water content 55.3 percent.

The concentrated solution emanating from the first filtrationissubjected for a period of 45 minutes at 95 C. to vigorous stirring inthe presence of 240 g of nickel (Ill) hydrate pulp containing 6.57percent of nickel. During this operation, the pI-I-value is kept atabout 4 by the addition of 300 ml of normal sulphuric acid. Followingfiltration in a Buchner and repeated washing of the precipitate withboiling water, 3,994 ml of a pure green liquor corresponding to thefollowing weight analysis are finally obtained:

Ni 70.37 g/l Co 0.025 g/] Fe 0.001 g/l M immeasurable traces Insolublecomponent less than 0.001 HNO: 0225 equivalent/liter The finalprecipitate weighs 568 g and contains 3.45 percent of nickel.

It was found that the Ni:Fe ratio initially 13.8 exceeds 70,000 in thepurified liquor, while the Ni:Co ratio which was 28.75 almost reaches3,000.

On the other hand, it was found that the other impurities such ascopper, manganese and silica were eliminated.

If a complete reckoning is made, allowing for samples taken, it will befound that 212 g of nickel in matte form, 125.7 g of nickel in carbonateform, and 17.3 g of nickel in hydroxide form, making a total of 355 g,were introduced. Of this total 295 g were found in the completelypurified solution. 9.5 g in the final cobalt (III) hydroxideprecipitate, 7.25 g in the ferric residues and 21.65 g in the liquorsused to wash the ferric residues.

Finally, the matte conversion yield during the oxidizing lixiviation isremarkably high at 99.9 percent.

EXAMPLE 2 On this occasion, a large laboratory apparatus in the form ofa -liter capacity glass reactor is used. The treatment is carried out on15.25 kg of a sulphurated compound emanating from the hydrometallurgicalrecovery of laterites having the following weight analysis:

Oxidation is carried out in 3 /2 hours with 49.42 liters of exactly llNcommercial nitric acid. Air is bubbled through the reactor at a rate of6 cubic meters per hour whilst its contents are stirred with a 3-bladepropellor agitator turning at 600 rpm. The temperature at the beginningof introduction of the matte was 54 C. It rises quickly, i.e., in lessthan 15 minutes, to around 75 C. and is kept at this value throughoutthe introduction period. After all the sulphurated compound has beenintroduced, the contents of the reactor are boiled for 30 minutes,followed by the addition of 30 liters of boiling water to dilute thereaction product. The residue weighing 1,290 g is filtered. It has thefollowing weight analysis:

H O 51.65% Ni 0.040% Co 0.002% S total 37.23% Fe 0.625% Cu 0.001% Mg0.225% Mn nil A1 0,, 0.14% SiO, 6.32%

jected to a treatment, in which it is deprived of iron, copper andcobalt before being concentrated and crystallized. Crystallization iscarried out by evaporation and most of the nickel is obtained in theform of crystalline sulphate. The crystals have the following weightanalysis:

Ni 21.1 1% Co 0.01 1% Fe 0.001% Cu 0.002% Mg 0.0287: Ca 0.18% SiO 0.015%A1 0.007% HNO 0.03% MnCrPb nil By contrast the mother liquors have thefollowing analysis:

Ni 157.37 g/l Co 0.014 g/l Fe 0.01 g/l Cu 0.001 g1 Mg 0.043 /1 Ca 2.42g/l sio 0.21 g/l A120, 0049 g/l HNo, 145.03 1

These mother liquors can be converted by precipitation with sodiumcarbonate, caustic soda and hypochlorite into carbonate and nickelousand nickelic hydroxide available for an operation of the same type,these reactants being used to eliminate the iron and the cobalt.

EXAMPLE 3 4.3 Kg per hour of a nickel matte having the following weightanalysis:

Ni Co (Combined) 74.98% Co alone 1.6% Fe 1.01% 5 22.00%

and 12 liters per hour of 50.7 percent recycled nitric acid, arecontinuously introduced into a 100-liter capacity reactor situated atthe head of a series of apparatus arranged in a cascade and consistingof components specially suited to each operation, more particularly:oxidation, sulphation and dentrification, hydration, elimination or ironand manganese, elimination of copper and cobalt, evaporation andcrystallization.

In addition, air is continuously bubbled through the reaction mixture ata rate of 6 cubic meters per hour whilst the contents of the reactor arevigorously stirred by means of a propellor stirrer with four blades each5 cm in diameter, turning at 650 r.p.m.

The temperature recording curves indicate that the temperature variesbetween 80 and 90 C.

The gases are delivered to the bottom of a three stage tower filled withRaschig rings in which the washing liquid circulates downwards, theadmission of air required for reoxidizing the nitrous vapours beingensured by inlets arranged at intervals along the tower which is placedunder a slightly reduced pressure. Ten to eleven liters per hour of a4446 percent nitric acid solution are taken from this nitric acidregeneration system and returned to the reactor after the addition ofenough fresh concentrated acid to restore the original concentration. 1

The brine which results from the oxidation regularly overflows into thesecond reactor in which concentrated sulphuric acid (66 B) is introducedat a rate of 1.5 liters per hour by means of a metering pump. Thetemperature is regulated to 105 C. The reddish fumes escaping from thisreactor are delivered to a main collector leading to the nitric acidregeneration tower.

The highly concentrated solution thus obtained is hydrated by theintroduction of 10 liters per hour of cold water and brought to the boilin a third reactor before being separated in a continuous centrifuge.

An average of 23 liters per hour of solution containing 137 g/liter ofNi Co and 320 g/liter of residue containing 19.8% of Ni Co are collectedat this stage.

The yield from the treatment is thus above 98 percent while the recoveryof nitric acid varies between 70 and percent.

The iron is removed as follows: the solution is adjusted to pH 5.5 bythe addition of a basic nickel carbonate pulp and is then filtered in apress. The amount of iron left in the solution is less than 5 ml perlitre. The filter cake which is rich in nickel is used for the initialremoval of iron from the solution to be worked up this treatment beingcarried out at pH 4 and at a temperature of 60 C.

By an average taken over 1 hours operation 23 liters of solutioncontaining 137 g/liter of Ni Co and 769 g of nickel carbonate pulpcontaining 13% of Ni, i.e. 3,249 g/hour of nickel and cobalt areintroduced, while 26.2 liters of iron-free solution containing 123g/liter of Ni Co and 307 g of ferric residues containing 5.54 percent ofNi Co are removed.

It is obvious that these ferric residues, poor in nickel, can becompletely deprived of nickel by reintroducing them into the sulphatesolution in a third treatment stage with a view to eliminating the iron.

Finally, the iron-free solution is subjected in two reactors whosetemperature is regulated to 100 C. to intensive stirring by means ofturbine impeller rotating at 2,200 r.p.m. in the presence of trivalentnickel hydroxide.

The first reactor receives the cake emanating from the centrifuging ofthe reaction product issuing from the second reactor, while a largeexcess of the oxidizing reactant is introduced into the second reactor.The following distribution is observed, calculated on an average of 1hours operation:

incoming solution 26.2 liters containing 123 g/litre of Ni Co and 905 gof trivalent nickel hydroxide pulp containing 10.97 percent of nickel;

outgoing solution 28 liters containing g/liter of nickel with less than10 mg/liter of residual cobalt and 598 g of filter press residuescontaining 5.85 percent of nickel and 11.54 percent of cobalt.

The solution is concentrated and crystallized in a continuous-cyclecrystallizer/evaporator. The crystal paste is centrifuged and thecrystallizate is clarified by spraying it with water.

An average of 12.8 kg/hour of crystals with the following analysis arerecovered:

Ni +Co (combined) 20.73% Co less than 0.005% Fe less than 0.001% No,less than 0.01%

and 4.2 liters of mother liquor containing 132.8 g/liter of Ni Co and6.2% of N0 The nickel present in this mother liquor is precipitated withsodium carbonate and sodium hydroxide in the presence of hypochlorite toform the reactants required for removing the iron and the cobalt.

The invention is not limited to the examples described above and inparticular although the presence of free oxygen during the oxidizinglixiviation phase is preferred it is not indispensable and the presenceof nitric acid alone is entirely sufi'rcient to convert the sulphidesinto sulphates.

We claim 1. A process for hydrometallurgically treating a nickelconcentrate containing from 55 to 75 weight percent of nickel, from 10to 40 weight percent of sulphur and minor proportions of secondarymetals, which process comprises the steps of:

i. subjecting said concentrate in comminuted form to an oxidizinglixiviation by means of nitric acid at a temperature lower than boilingpoint, said lixiviation being carried out, while stirring, at theatmospheric pressure and in the presence of air with such an amount ofnitric acid that it forms a suspension containing between 45 and 67percent by weight of said concentrate, the nitrous vapours formed duringsaid oxidizing lixiviation being regenerated into nitric acid andrecycled,

ii. subjecting said suspension to a sulphation by the addition of enoughsulphuric acid to produce, after filtration, a solution of nickel in theform of a true sulphate,

iii. subjecting said solution to successive treatment stages to removesaid secondary metals as follows: a. treating said solution with nickelcarbonate at a pH between 4 and 6 to precipitate the iron in the form offerric hydroxide and ferric carbonate which are separated by filtrationfrom said solution,

b. treating said solution with nickel powder to remove the copper bycementation,

c. treating said solution with nickel (lll) hydroxide at a temperatureof from 80 C. to boiling point over a period of from minutes to 2 hoursto precipitate the cobalt in the form of cobalt hydroxide which isseparated from said solution by filtration,

iv. subjecting the solution which results from said steps iii and whichcontains nickel as substantially the only remaining cation, to anevaporation-crystallization treatment, whereby pure hydrated nickelsulphate crystallizes from a remaining mother liquor solution,

v. separating said pure crystalline hydrated nickel sulphate from saidmother liquor, and

vi. treating said mother liquor with sodium carbonate to precipitatenickel carbonate which is recycled to said iron separation stage iiiaand treating said mother liquor with sodium hypochlorite and causticsoda to precipitate nickel hydroxide which is recycled to said cobaltseparation stage iiic.

2. A process as claimed in claim 1 in which said nickel concentrate isnickel matte crushed to a powder of which by weight of the particles arebetween and 200 microns in size.

3. A process as claimed in claim 1 in which said nickel containingconcentrate is a dispersed pulp produced by a wet precipitationtreatment.

2. A process as claimed in claim 1 in which said nickel concentrate isnickel matte crushed to a powder of which 80% by weight of the particlesare between 100 and 200 microns in size.
 3. A process as claimed inclaim 1 in which said nickel containing concentrate is a dispersed pulpproduced by a wet precipitation treatment.